Flexible shipping container



Malch 23, 1954 w. PR G R 2,672,902

' FLEXIBLE SHIPPING CONTAINER Filed Feb. 1, 1952 v 2 Sheets-:Sheet 1 I N V E TOR. 404 4/4/ 7 P/iAZ-f? ATTORNEY March 23, 1954 w PRAGER FLEXIBLE SHIPPING CONTAINER Filed Feb. 1, 1952 2 Sheets-Sheet 2 X a -C7' k P a n P E 7 INVENTOR.

ATTORNEY Patented Mar. 23, 1954 PATENT OFFICE FLEXIBLE SHIPPING CONTAINER William Prager, Hoxsie, It. I., assignor to United States Rubber,Company, New York, N. Y., a corporation of New Jersey Application February 1, 1952, Serial No. 269,461

14 Claims. (Cl'. 150-05) This invention relates to flexible shipping containers and more particularly to collapsible shiping containers which preferably are made of rubber coated cord fabric that are adapted to be pressurized in use.-

A flexible shipping container and. a method of making this container are disclosed and claimed in the copending Cunningham applications Serial No. 131,407, filed December 6, 1949, now Patent No. 2,612,924, issued October '7, 1952, and Serial No. 144,523, filed February 16, 1950, now Patent No. 2,613,169, issued October '7, 1952, respectively. This Cunningham container is made of rubber coated cord fabric and has a generally cylindrical body and fiat convex-concave ends which are connected and held concave by a central cable that limits the distance between these ends. In use, the: Cunningham barrel is filled with a liquid or dry material to be shipped or stored, and it may be internally pressurized by air or another suitable gas so that it is in a sense inflated and hence substantially rigid. This pressurized container which is substantially cylindrical may be handled and stored in the same manner that metal barrels are handled and a ningham construction, it is a desirable one for flexible containers, and it is an object of the present invention to provide an improved form of this Cunningham construction for flexible containers. More particularly this invention contemplates a container utilizing thev Cunningham construction, in which full advantage is taken of the strength characteristics of the material formin thewalls of the container. The exact construction 1' disclosed in the. above-mentioned patents is such that when the container'is 'presui-iced, compressive and bending stresses may be induced in container walls near the ends of thecontainer by the internal pgressure. These stresses tend to deform or wrinkle the flexible material forming the walls of the container and t thereof remains substantially constant throughout the greater portion of the container. A still further object of this invention is to form such a container having the cords of the fabrics forming the plies arranged so that full advantage is taken of the unidirectional strength of the cord fabric forming the walls of the container.

These'objects are achieved by substituting for the flat end container heretofore used, a container having elongated end portions which taper inwardly gradually toward the longitudinal axis of the container. Since the ends taper gradually, the effective area of the end portion available as a base when the container is placed on end, is reduced slightly, but this is still sufficiently large to provide a stable body when it is so positioned. When the ends are elongated, however, it is possible to eliminate sharp curves from the container body surface, and when this is'done the container may be made free of compressive stresses. Although the resultant container is not precisely cylindrical, for the elongated cnd portions have a gradual inward taper, it is substantially so because for practical purposes the gradually tapered end portions constitute a containuation of the cylindrical body portion; consequently the practical advantages of the Cunningham cylindrical container are achieved in a container which is free of compressive stresses.

Bending stresses are eliminated from the container by forming it in such a manner that the radius of curvature of a meridian through the container does not vary discontinuously. As will be pointed out more fully hereinafter, this is of particular importance at the circles where the end portions join the body portion of the contamer. A practical"construction which eliminates bending stresses at this circle, and which provides agradual' taper for the end portion, is one in which the surface of the end portion is in the form of a fifth order parabola. Other constructions which would satisfy these requirements are parabolic curves of the third or seventh order, although as will be pointed out, curves of this nature have certain disadvantages which make them less desirable in barrel constructions.

Since the container of this invention is substantially cylindrical, it has the great utility of the Cunningham cylindrical construction; but since the end portions of the container are elongated gradually tapering members, the container may be made free of bending and compressive stresses caused by pressurization of the container.

Inasmuch as these latter forces tend to weaken flexible containers, a flexible container constructed according to this invention will have a much longer useful life than those heretofore constructed, and it will be better able to Withstand internal pressure and the abuses to which it is subjected in ordinary usage. This latter advantage of the container of this invention is particularly important, for these containers are intended to be used in railway shipment where they will be subjected to very rough usage.

For a better understanding of these and other characteristics and advantages of the present invention, reference should be had to the following description and the accompanying drawings; wherein,

Fig. 1 is a side view of the container of this invention having a portion of the outer ply of cord fabric broken away to show the disposition of the cords of an underply of fabric in the container walls;

Fig. 2 is a sectional view of a part of an end of the container of this invention;

Fig. 3 is a perspective view of a portion of the cord fabric forming the walls of the container of this invention;

Fig. 4 is a diagrammatic sectional view of a median layer of material forming the end portion of the container;

Fig. 5 is a view similar to Fig. 4 of an end portion of a flat end container heretofore used;

Fig. 6 is a diagrammatic view of a loaded string used for purposes of analysis;

Fig. 7 is a diagrammatic perspective view of a segment of a median layer of fabric of the end portion of a container; and

Fig. 8 is a diagrammatic view of a single mesh of the cord fabric in the body portion of the container of this invention.

Referring to the drawings and to Figs. 1, 2 and 3 in particular, there is shown the flexible shipping container of this invention having a. cylindrical body portion Hi and elongated convexconcave end portions II and I2. A fill opening 13 is disposed in one end of the container, and fix- +4 tures 14 consisting of outer plates l5 and inner plates I 6 grip the fabrics of the end portions. The nuts and bolts I! serve to compress the fabric of the end portions between the plates l5 and I6, and to fix the straps I9 and lifting eyes 20 to the container. Joining the fittings i4 and holding the end portions dished at their center is a cable l8 of rope or wire or other suitable material of such a length as to be just slack when no pressure differential exists across the walls of the container. it

The walls of the container are formed of a plurality of layers of cord fabric 2 I, in which each layer is formed of closely spaced warp yarns 22 and loosely spaced weft yarns embedded in rubber 23. Since a single layer of this fabric has strength in the warp direction only, several plies are used to build a wall in which each ply has its warp yarns placed at a substantial angle to the warp yarns of the adjacent layers so that the wall has two directional strength. This construction is well known in the tire industry. The inner and outer layers of cord fabric of the walls of the container preferably are coated with surface layers of rubber or other suitable material to protect the cord fabric against the material to be shipped in the container as well as against external abrasions. The container walls may be built up by the method disclosed in the above mentioned method Patent 2,613,169, or by any other suitable method, but the fabric forming the body portion of the container is made of such a length that the seams 24 and 25 fall along the end portion of the container a substantial distance from the body portion for a reason which will be more fully pointed out hereinafter.

Referring now to Figs. 1 and 4 there is shown a container according to this invention having elongated convex-concave end portions, and in particular a container having the shape of a body of revolution in which, a meridian through the end portions conforms substantially to a, fifth order parabola between the point a where the end portion joins the cylindrical body portion and the point D; from the point I) to the point d where the fabrics of the end portions enter the fittings M, the end portions are shaped in the form of a circular are. For an understanding of the advantages of this form of a container, consider Fig. 4 and the stresses on a generic point P on an end portion of the container when it is pressurized with an internal pressure p.

The fabric of the container wall at this point is subjected to three principal directional stresses which are (l) the stress along the tangent of the meridian of the container which passes through P; (2) the stress along the tangent of the parallel circle of the container which passes through P; and (3) the normal of this surface at P. This last stress is principally compressive and varies in intensity from p at the inner surface of the layer to zero at its outer surface. It will be seen that the other two principal stresses are considerably larger than this compressive stress, hence it can be ignored. To find the meridional stress resultant M per unit length of the parallel circle, consider the vertical equilibrium of that portion of the fabric bounded by the parallel circle through P and the topmost parallel circle. In Fig. 4 this portion is represented by the arc PQ. Since only horizontal forces are trans mitted across the topmost parallel circle, under equilibrium conditions the vertical resultant of the forces transmitted across the parallel circle through P must equal the vertical resultant of the pressure forces acting on the considered portion of the lid. With the notations of Fig. 4 this condition takes the form 1 shown in the figure for the radius of curvature,

the tension on the .string, and the central angle, the forces s acting on this string at K and F have the resultant of magnitude Sdo directed from the midpoint of the arc KF towards O".

s The equilibrium of this string requires therefore As a rule an element of the fabric forming the end surface of the container will have a double curvature. Consider the portion GPIJ of this aeraeoc surface shown in Fig. .5 GP and L] are elements of two neighboring meridians or axial sections, and GJ and PI are elements of two neighboring parallel circles, i; e. theciroles defined by the intersection of the container walls and planes at right angles to the container axis. The normals of the surface at theadjacent points G and P of the meridian intersect in the first center of curvature O, and'the normals of the surface at the'adjacent points P and Iof the parallel circle intersect in the second center of curvature O which lies on the axis of the container. OP and 07-1 are the principal radii of curvature at the point P of the surface; they are denoted T and L respectively in Fig. 7. If M and N denote the meridional and circumferential stress resultant per unit length of the parallel circle and meridian respectively) the equilibrium of the elements shown in Fig; '7' reduiresthat This equilibrium condition is an obvious generalization of the simpler condition of Equation 2 which is valid for a string. The dotted center in the part of the container end shown in Fig. '7 may be visualized as elements of two strings; the meridional string is under tension M and carries the portion T at this load 1:; the other string is under the ten- 'sion N and carries the remainder sin W Substitution of these-values; and the value of M given in Equation 1 in Equation 3, and solution for N gives *2 sii1 W[ 2kg si'n W Equation 4 shows that N Will vary discontinu ously whenever the radius of curvature of the meridian and hence g varies discontinuously.

Since discontinuities in stress cannot actually arise in the container wall, bending forces are induced; and if it is to withstand these bending forces thecontainer wall should be, reinforced where they occur.

Furthermore since M remains continuous, and since the proper cord angle depends on the ratio M /N as will be pointed out more fully below, if N varies discontinuously in any areaof the wall, the optimum cord angle varies discontinuously. As a practical matter. the cord angle can-- not be made to vary in the container walls, hence a container in which the radius of curvature varies discontinuously does not utilize the strength characteristics of the cord fabric or the walls efficiently. Further, itiS neither G0nOmical nor acceptable to reinforce the walls of flex ible containera for to do so increases both mate of the container.

Bending stresses may arise at any point on the container wall, but they normally occur-at the parallel circles where one meridional curve joins another. At'these circles, the two curves should have the same radii of curvature. Thus where the. end portions join the cylindrical body portion, a meridian through the former should have an infinite radius of curvature. By making a container having elongated rather thanflat end portions. discontinuities in theradiusof cur. vature may be eliminated; yet the container may be given a shape which is substantially cylindrical.

Equation ,4 signifies further the condition under which compressive stresses will be inducedin the walls of the container,- for if the value in the brackets of this equation becomes negative, N becomes negative. Primarily this signifiesthat sharp curves must be avoided inthe container. Thus, consider the point P on the wall shown in Fig. 5. It will be. observed that the approxi mate values of k, W; and g atthis point'are .9, and .2 respectively, while 0' equals .55; The expression in brackets of Equation 4 becomes .992, and the container wall at the point P is subjected to compressive forces.

I have, found that sharp curves may be eliminated from a container which has a substantially cylindrical shape if elongated convex-con cave end portions are substituted forthe flat end portions heretofore used in cylindrical containers. One practical construction of a substantially cylindrical container in which the fabric of the walls is notsubjected to'bending or compressive stresses consists of acontainer"hay ing a cylindrical bodyportionand end portions which are shaped throughout a part of their length adjacent the body portion in-the shape of a fifth order parabola curve, and throughout the remainder thereof in the shape of a circular arc.

A satisfactory container of this type is-one in which the end portions are shaped so that a meridian therethrough between the points a and b of Fig 4 conforms substantially to the cone. tion ass ss s-t)" a and between the points I) and d to a circulararc of radius .2863D. Point b has the coordinates gazAD and 1 110240, and point a is the-origin. In this equation :11 is the distance from a.-proiection of the cylindrical body portion to the, sur face of the end portion and a; is the distance from the point of intersection of the end and; body portions to the surface of the end portion as in-; dicated inFig. 4.. Some representative points on this end portion and the meridional and circumferential stress resultants in termsof pDobv- In the above table points 0 andi'loorrespond to points a and b respectively. From point D to point 6!,- since this is an arc of a circle, N remain constant and M increases toward infinity which would occur at a point of intersection on the container axis between the arcs of the two circular curves forming the right and left parts of the end portions. To avoid the unreasonably large stresses which would occur near the longitudinal axis of the container, the fabric of the end portions is gripped by the fixtures M at the circumferences of the plates [5 and I6. To further reinforce the end portions in this area of increased strain an additional ply of heavy cotton duck 26 may be bonded to the cord fabric of the end portions. The ratio of the diameter of the parallel circle of maximum end projection to the diameter of the cylindrical body portion of this container is .395, and the maximum end projection is .4815D.

From the foregoing table it will be seen that up to the point 2, a distance equal to roughly /3 of the maximum projection of the container ends, the ends depart only minutely from cylindricality, and that up to the point 7, where the end projection is more than its maximum value, the departure of the container end from cylindricality is only about /5 the radius of the container. Thus this exemplary container is substantially cylindrical throughout most of its length. The effective diameter of the container base is approximately .4 the maximum diameter of the container; so that the container is stable when placed on end. The above table for this container shows further that the walls at no point are subjected to compressive forces. Furthermore, since the end has the shape of a fifth order parabola near the cylindrical body portion, an inflection point occurs at the intersection of these portions, and the container is free of bending stresses at this circle of intersection. Further, the circular arc has a radius of curvature equal to the radius of curvature of the parabolic curve at the intersection of these curves, so that the radius of curvature of a meridian of the container does not vary discontinuously.

Although the curve described here does not require a particular size of container, a satisfactory size is one in which the body portion has a length equal to its radius. Thus, a 55 gallon container in this size would have a diameter of 23 /g This container size is compact, stable and easy to handle; hence it is an extremely desirable shipping container.

To determine the proper cord angle in the cylindrical body portion of the container consider Fig. 8. The sides AB and CE are small segments of neighboring parallel circles, and the sides AC and BE are small segments of neighboring generators of the cylindrical body portion. If the lengths AB and AC are denoted by e and respectively, the total axial and circumferential stresses acting on the cordmesh shown are Me and Nf respectively. These 'forcesmay be visualized as acting at the centers of AB and AC where the cords of the fabric overlap. Let U denote the product of the force in a typical cord by the number of plies having cords in the same direction. Vertical equilibrium at the center of AB requires Me=2U sin Z (6) and horizontal equilibrium at the center at AC Dividing 6 by '7 and substituting 8 gives and Substituting these values of M and N in Equation 9 gives tan 2:

Thus the cord angle in the cylindrical body portion depends only upon the ratio of radius of the circle of maximum end projection to the radius of the cylindrical body portion. For the typical container given above, the value c=.395 and Z=33.

From a comparison of Equations 12 and 9, it will be apparent that although the cord angle in the cylindrical body portion is constant and depends only upon the ratio c, the optimum cord angle for any part of the end portion will vary with the values of the ratio M/N at that point. Since as a practical matter the cord angle of the fabric forming the walls of the container cannot vary, if the angle determined by Equation 9 differs materially from the angle determined by Equation 12 the fabric of the container walls is being used inefiiciently. A comparison of the above table with the requirements of these equations reveals another important advantage of the container shape prescribed by that specific embodiment. The optimum cord angle for the fabric of the end portion as determined by the ratio M /N varies from 33 at the cylindrical center portion to approximately at point 4; in effect for practical purposes the cord angle is substantially constant up to the point 4, and this optimum cord angle is substantially that required by the cylindrical body portion. Thus, if the seams 24 and 25 are placed at or near the parallel circle passing through the point 4 the cord fabric forming the body portion will be used most efficiently. It will be noted further that the minimum value of M, which determines the strain on the seam, occurs at the parallel circle through point 5. However, between point 5 and point 4 the meridional stress varies less than 1%; hence, the seam may be placed at that circle which permits the most eflicient use of the fabric forming the container walls.

From the foregoing it will be apparent that I have devised a shipping container which has a good practical construction in that it may be handled, stored and shipped easily, yet which will give greatly improved wearing qualities and should have a very long life in use. In particular a container may be made which has a substantially cylindrical shape, yet which is free of bending or compressive, or both bending and compressive forces. These advantages are achieved by abandoning the flat end portion and substituting in its stead the elongated end por- 9T tion :of thc present invention which is well adapted to resistinternal pressures.

Although a specific embodimentof-a container according to this-invention has been described, changes may be madein the constructional details without departing from the spiritorscope of this invention. In particular, although a specific fifth order parabola curve has been described-other curves maybe devised within the teaching of this invention without departing from the spiritor scope of the invention.

Thus, althougha fifth ordercurve has been describedother curves which provide a gradually inwardly tapering end portion may besubstituted therefor, so long-as sharp curves are eliminated from the end. Further, other curves are known which'could besubstituted for the fifth order parabola to provide an inflectionpoint at the circles where the ends meet the body. Thus, parabolic curves of the third or seventh order wouldeliminate bending stresses in this area. However, in general these curves require rather sharp curves near the centers of the end portions so that compressive stresses occur. If inparticularcircumstancesthese stresses are not objectionable, these curves may be used advantageously in a container end,

Although in the description of the curve of the specific embodiment illustrated, a single layer of fabric is described; it will be appreciated that, as s'hownin Figs, -1 and 2, the walls of the contain'er are made up of several layers of cord 'fabric; in no event less than two, and that a container according to this invention would have its walls conforming substantially to the desired curve.

-Having thus described my invention, what I claim anddesire to protect by Letters Patent 1. A collapsible container designed to be pressurized in use, comprising a cylindrical body portion, two end portions and means holding said endportions dished centrally of their .parallel circles of maximum end projection, each said end portion being shaped such that a container meridian therethrough conforms substantially to the curve aci er er j nected to said end portions, wherein is the distance from the plane formed by the intersection of the cylindrical body portion and the end portion to the meridian through the'end portion, and wherein y is the distance from a projection of the cylindrical body portion to the meridian through the end portion, and D is the diameter of the cylindrical body portion of the container, whereby the container walls are subjectedztoonly tensile stresses when the container is pressurized.

2. A collapsible container formed of coated cord fabric. and designed to be pressurized in use, comprising acylindrical body portion having a'length approximately equal to its radius, two endsiportions, means embracing each said end portion at :i-tsv center, and a came connecting said means and holding the end portions-dished centrally of theirilpar'allel circles of maximum.

end projection, each said end portion. bein to" shaped such that a container meridian therethroughconforms substantially to the curve between the pointscc=l and 'cs.=. .iD and to the arc of the circle of radius 286313 from the point x.=;4D to the'point where said, means embraces said end portion, wherein a: is the distance from the plane of intersection of the end portion and the cylindrical body portion to the meridian through the'end portion, y is the distance from a projection of the cylindrical body portion to the meridian throughthe end portion, and D is the diameter of the container, whereby the cord fabricis subjected only to tensile stresses when the container. is pressurized;

3. A collapsible container designed to with stand high internal fluid pressures, comprising a cylindrical body portion and two elongated rounded end portions formed of a plurality of layers of coated cord fabric wherein the cords of one layer form an angle with the cords of adjacent layers, said containerbeing formed so that internal pressures subject the walls thereof to tensile stresses only, means holding said end portions dished centrally of their parallel circles of maximum end projection, each said end portion conforming substantially to the curve end portions'formed of a plurality of layers of coated cord fabric wherein the cords of each layer form a substantial angle with the cords of adjacent layers, means holding said end portions dished centrally of their parallel circles of maximum end projection, said container being shaped so that internal pressures subject the walls thereof to tensile stresses only, each said end portion conforming substantially to a fifth order parabolathroughout a portion of its length.

adjacent to the body portion, and having a paraallel circle of maximum end projection whose diameter is approximately .4 the diameter of the body portion.

5.. A collapsible shipping container designed to withstand high internal hydraulic pressures, comprisinga cylindrical body portion and convexconcave end portions formed of a plurality of layers of coated cord fabric in which the cords of one layer are angularly disposed relative to the cords of adjacent layers, means holding said end portions dished near their centers, said end portions being formed such that the fabric forming thewalls of the container is subjected to only tensile stresses when the container is pressurized internally and being formed throughout a sub- I stantial portion of their lateral projection adjacent to the cylindrical body portion substantially in the shape of a parabolic curve.

6. A collapsible shipping container designed to be pressurized in use, comprising a cylindrical body portion and two elongated endportions formed of coated cord fabric, said end portions having a gradually inwardly tapering confiuration from the circles where they join said center portion to a parallel circle of maximum end projection, and a dished configuration centrally of said parallel circle, said end portions being formed so that the walls of the container are free of bending and compressive stresses induced by internal pressurization, and means joining said end portions and holding them dished centrally of said parallel circle.

7. A collapsible shipping container designed to withstand high internal fluid pressures, comprising a cylindrical body portion and elongated convex-concave end portions, a first multiply coated cord fabric forming the cylindrical body portion and a part of the end portions, additional multiply cord fabrics forming the remainders of the end portions, means joining said additional fabrics and holding the end portions dished centrally of their parallel circles of maximum end projection, said end portions being shaped such that the optimum cord angles required by the stresses induced by internal pressures in the container in the parts of'the end portions formed by said first fabric are approximately the same as the optimum cord angle required by the stresses in the cylindrical body portion, and wherein the seams formed by said first fabric and by said additional fabrics lie near the parallel circle of minimum meridional stress of the container.

8. A collapsible shipping container designed to withstand high internal fluid pressures, comprising a cylindrical body portion and convexconcave end portions shaped so that internal pressures subject the Walls of the container to tensile stresses only, a first multiply coated cord fabric forming the body portion and a part of the end portions, additional fabrics forming the remainder of the end portions, means holding said end portions dished centrally of their parallel circles of maximum end projection, said'end portions being formed so that the values of M and N in those parts of the end portions formed by said first fabric are such that the angle whose tangent is /M/N is substantially the same as the angle whose tangent is wherein M is the meridional stress resultant, N is the circumferential stress resultant, and c is the ratio of the diameter of the parallel circle of maximum end projection of said end portions to the diameter of the cylindrical body portion.

9. A collapsible container designed to withstand high internal hydraulic pressures, comprising a cylindrical body portion, elongated convexconcave end portions, a first coated cord fabric forming said body portion and a part of said end portions, additional fabrics forming the remainders of said end portions, means holding said end portions dished centrally of their parallel circles of maximum end projection, said container being shaped such that internal pressures subject the walls thereof to tensile stresses only, and said first cord fabric being disposed so that the cords thereof form an angle with a plane at right angles to the longitudinal axis of the container whose tangent equals whereinc isthe ratio of the diameter of the parallel circle of maximum end projection to the diameter of the cylindrical body portion.

10. A collapsible container comprising a body portion formed of coated cord fabric, end portions formed of coated cord fabric, said end portions being shaped such that a container meridian therethrough conforms substantially to a curve having the equation y=Aac -Br +C:c wherein y is the distance from a projection of the cylindrical body portion to the meridian through the end portion, a: is the distance from the plane of the intersection of the end portion and the cylindrical body portion to the meridian through the end portion, and A, B and C are constants determined by the diameter of the body portion of the container, throughout a substantial portion of the end projection of said ends near said body portion, and said end portions being formed such that a meridian therethrough conforms substantially to the shape of a circular are from the terminus of said curve to at least the parallel circles of maximum end projection, and means internally of the container fixed to said end portions and connecting them, said means being fixed to said end portions inwardly of said parallel circles of maximum end projection.

11. A collapsible container, comprising a sub stantially cylindrical body portion, two elongated convex-concave end portions, each said end portion having a radius of curvature at the parallel circle where it joins said body portion equal to the radius of curvature of said body portion at said parallel circle, a meridian through said end portions conforming substantially to the shape of a parabolic curve throughout a substantial portion of each end portion adjacent said parallel circle, and means connecting said end portions fixed to each end wall of the container centrally of the parallel circle of maximum end projection of the end portions holding said container against longitudinal expansion.

12. A collapsible container, comprising a body portion, two end portions, the wall of said container lying substantially along a meridian through each said end portion that conforms substantially to a parabolic curve throughout the part thereof adjacent said body portion and to a circular are from the parallel circle of termination of-said parabolic curve to a parallel circle beyond the parallel circle of maximum end proj ection of said container, the radius of curvature of said meridian through said end portions varying continuously across the parallel circles where the body and end portion join and where the parabolic curve and circular arc join, and means connecting said end portions fixed to each end wall of said container centrally of the parallel circle of maximum end projection holding said container against longitudinal expansion.

13. A collapsible container, comprising a body portion, two end portions, the wall of said container lying substantially along a meridian through said end portions that conforms substantially to l a fifth order parabolic curve throughout each end portion adjacent the body portion and to a circular are from the parallel circle of termination of said parabolic curve to a parallel circle beyond the parallel circle of maximum end projection of said container, the radius of curvature of said meridian through said end portions varying continuously across the parallel circles of the container where a transition from one curve to another occurs, and means connecting said end portions fixed to each end wall of the container centrally of the parallel circle of maximum end projection holding said container against longitudinal expansion.

14. A collapsible container, comprising a wall formed of a plurality of layers of coated cord fabric, said layers being disposed with, cords in adjacent layers at an angle to each other, the wall of said container lying substantially along a meridian through said container at each end of the container that conforms substantially to a fifth order parabolic curve throughout a substantial portion of the container wall on each side of the axis of the container, the wall of said container being dished inwardly at each end thereof centrally of the parallel circle of maximum end projection, and means fixed to the wall of said container at each end thereof centrally of said parallel circle of maximum end projection holding the portion of the container wall to which said means are fixed depressed inwardly of said parallel circle of maximum end projection.

WILLIAM PRAGER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 18,035 Borrman Aug. 25, 1857 1,256,428 Baumann Feb. 12, 1918 1,554,316 Winship Sept. 22, 1925 2,287,824 Pihl et a1. June 30, 1942 2,381,739 Gray Aug. 7, 1945 2,612,924 Cunningham Oct. 7, 1952 

